Elastomeric articles formed from natural latex emulsions have been used in the past in many different applications including surgeons gloves, examining gloves, prophylactics, catheters, balloons, tubing, and the like. Natural rubber latex has been useful in the production of such articles in part because of its physical properties upon curing. For example, the articles may exhibit very elastic properties. The articles formed not only may be stretched many times their length, but are also capable of substantially returning to their original shape when released.
One problem encountered with natural rubber articles in the past is that the natural latex may contain proteins which cause reactions, such as allergic reactions, in consumers who come into contact with the materials. In response, industry and governmental standards have been set requiring the level of protein remaining in the latex after production to be quite low, generally less than 50 micrograms/gram (xcexcg/g), and levels of antigenic protein below about 10 micrograms/square decimeter (xcexcg/dm2). Methods have been developed to meet these standards, including rather complicated chlorination processes involving the use of chlorine gas or liquid such as sodium hypochlorite. These processes present their own difficulties, however, including high associated costs and difficulties in dealing with the corrosive materials. As such, a relatively inexpensive, safe method for reducing the amount of protein in natural latex articles is needed.
Traditionally, natural latex articles have been manufactured through the use of a mold or former in the shape of the article to be produced. For example, when manufacturing a glove, a hand-shaped mold or former is first dipped in a coagulant. After the coagulant has dried on the former, the former is dipped in a natural latex such that a coating is coagulated on the former. The latex is then cured and the formed natural rubber article may be stripped from the mold, which may also invert the glove. In some cases, the former may be dipped into a slurry prior to stripping, in order to prevent blocking of the film upon stripping.
Elastomeric articles are typically tacky to the touch when initially manufactured. Tackiness at the surface of the article may increase the difficulty in stripping the product from the mold during manufacture. Historically, the most common process for decreasing tackiness of the glove has been the addition of a powder such as calcium carbonate to the coagulant used when forming the glove and to the pre-strip slurry. The powder acts as a buffer or barrier between the surfaces to help in preventing the film from adhering to the former during the curing process or to help in preventing the film from blocking to itself. A certain amount of this powder, however, may remain on the surface of the glove after it has been stripped from the former. While powder on the glove surface is acceptable for some applications, powders may not be desired in certain applications, such as surgical or other clean-room type applications.
As a result, post-stripping powder-removal processing techniques have been developed. For example chemical surface treatments such as chlorination have been developed in order to eliminate powders on the product after it has been stripped from the former. However, these powder-removal techniques tend to not only be expensive, but may also reduce the shelf life of the treated elastomeric article.
Another problem experienced with elastomeric articles which have been subjected to chlorination processes is that the outer gripping surfaces may become too slippery, and the wearer may find it more difficult to grasp objects in the gloved hand without losing the grip. This problem is particularly troublesome for gloves treated by powder-free processing techniques such as halogenation, because the very processing which removes the powder used to reduce tackiness on the surface of the glove may also react with the natural latex and promote excessive loss of gripping ability.
Thus, a need also exists for a method of producing a powder-free natural latex article which may be easily stripped from the forming mold and maintains good gripping characteristics.
In one embodiment, the process of the present invention is directed to a method for reducing the amount of extractable protein in a natural latex article. More specifically, the process of the present invention includes contacting a natural latex article with a solution comprising the ionic species of a disassociated metal salt. For example, a natural latex article, such as a glove, may be contacted with an aqueous rinse solution comprising the ionic species of sodium chloride for a sufficient amount of time such that the amount of extractable protein in the article is lowered to less than about 50 xcexcg/g. In one embodiment, a natural latex article may be contacted with a sodium chloride rinse solution.
In an alternative embodiment, the process of the present invention is directed to a process for producing a natural latex article, for example a glove. In this embodiment, the process may include contacting a former with a coagulant composition, and then contacting the former with a natural latex emulsion. The natural latex then coalesces on the former, and it may then be cured to form the article. After the latex is cured, the article may be immersed in the rinse solution of the present invention for a long enough period of time to cause the protein levels in the article to drop to acceptable levels. For example, extractable protein levels may be lowered to less than about 45 xcexcg/g through the process of the present invention.
Any metal salt which will not react with the polymer matrix forming the latex film may be used to form the rinse solution. For example, any Group I or Group II metal salt which will not react with the polymer matrix forming the latex film may be used. If desired more than one salt may be combined together in forming the solution.
In one embodiment, a powder may be added to the coagulant or to a pre-strip slurry, for ease in stripping the article from the former. For example, a calcium carbonate powder may be included in the coagulant and the slurry.
The natural latex article may be a powder free article, even when a powdered coagulant is employed, because the rinse solution may not only lower protein levels in the article, but may also remove residual powders, such as calcium carbonate powder, from the article.
A natural latex glove produced by the process of the present invention may have protein levels below about 45 xcexcg/g, antigenic protein levels below about 5 xcexcg/dm2, residual calcium carbonate levels of less than about 0.04 mg, and need not be subjected to a chlorination process. As such, the exposed natural rubber on the article will not be too slippery and may therefore provide a good gripping surface on the article.